Detection of unauthorized removal of theft detection target devices.

摘要

An article surveillance system includes a first monitor 26 at a store exit way 12 and second monitors 34 in the dressing rooms 20 and rest rooms 22 in the store to detect security tags 24 attached to articles of merchandise 14. When the tags 24 are attached to the merchandise they hold a ring 82 against the tags causing them to have a high resonant frequency which is detected by the first monitors 26 but not the second monitors 34. If the tags are removed from the merchandise in a dressing room or rest room, the ring falls away from the tag and its resonant frequency lowers and the tag is then detected by the second monitor 34.